The advancement of television technique has reached a level of implementing a device for displaying a stereoscopic image. Various stereoscopic image display schemes have been proposed, and at a time when the present invention was filed, a full-fledge commercialization of a stereoscopic type 3D television was at hand. In a stereoscopic 3D system, two images are captured by using two image sensors which are away from each other by about 65 millimeters, just like the human's eyes, and the captured images are transmitted as a broadcast signal to a receiver. Then, the receiver makes the two images inputted to left and right eyes of a viewer (i.e., a user), thereby simulating binocular disparity to allow for a depth perception and stereoscopic vision.
In the stereoscopic display device, two images, namely, left and right images, constituting a pair of stereoscopic images are accurately inputted to the left and right eyes of the viewer. That is, the two images are prevented to be simultaneously inputted to any one of the two eyes to cause interference. A method for preventing interference includes a polarization method, a time-sequential method, and the like. In the polarization method, a phase modulation plate is mounted on a display panel to allow left and right images to have mutually orthogonal polarization, an a polarization filter mounted in polarization glasses put on by the user makes left and right images inputted only to left and right eyes. In a time sequential method, left and right images are alternately displayed on the display panel. In this case, when a left image is displayed, only a left-eye shutter of active glasses put on by the user is open, an when a right image is displayed, only a right-eye shutter is open, thereby allowing left and right images to be inputted only to the left and right eyes, respectively.
However, it is not appropriate to provide a PIP function to the stereoscopic type 3D television because the PIP function may hamper the presence (or a sense of realism) of 3D images. As a result, every viewer must view the same 3D images. Meanwhile, a method for providing a supplementary function to a display device by using the characteristics of simultaneously displaying two images constituting a pair of stereoscopic images has not been proposed yet.
Also, in case where only some contents are provided as 3D while the other contents are provided as 2D at the early stage of 3D broadcasting, or in case where contents created as 2D in the past are broadcasted, it may not be proper to display 2D contents according to the 3D scheme. Thus, a method for displaying an image both as a 3D image and as a 2D image according to types of contents or according to a user selection is urgently required.